move private function to appropriate place
move private function to appropriate place

https://crrev.com/c/1806638/4/appengine/swarming/server/task_scheduler.py#1013

Change-Id: Id22de8aa57c95fdc47c67cd5d7064cec31614467
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1812539
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>
Auto-Submit: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py